Photoinduced Halogen-Atom Transfer (XAT) by N-heterocyclic carbene boryl radicals for C(sp3)−C(sp3) bond formation

12 August 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


In the realm of radical chemistry, halogen-atom transfer (XAT) is emerging as a powerful activation strategy in synthetic endeavors to engage otherwise recalcitrant organic halides. Although toxic tin radicals have been in the spotlight as halo-gen abstractors for decades, the era of photocatalysis has brought to light more sustainable options. Herein, we present a comprehensive study on the use of ligated boryl radicals to enable C(sp3)−C(sp3) bond forming reactions via XAT from alkyl halides. Two strategies have been developed using either direct light activation with near UV or photoredox conditions with visible light; both pivoting on N-heterocyclic carbene (NHC) boryl radicals. The present XAT strategy is very mild and accommodates a broad scope of alkyl halides, including medicinally-relevant compounds and biologically-active molecules. The key role of NHC boryl radicals in the operative reaction mechanism has been elucidated through a combination of ex-perimental, spectroscopic and computational studies.


Halogen-atom transfer
ligated boranes
boryl radical
visible light
radical chain carrier

Supplementary materials

Supporting Information
Experimental procedures, characterization data of synthesized compounds, copies of NMR spectra, complete mechanistic investigation. This material is available free of charge via the Internet at The primary NMR FID files for starting materials, compounds 3-53, as well as optimized geometries of species displayed in Figure 5E, IRC and PES profiles are available in the FigShare repository at 10.21942/uva.20459517.


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